Linear guide device

ABSTRACT

A linear guide device includes: a plurality of rolling elements; a guide rail extending in an axial direction thereof and including a plurality of rolling element rolling grooves in two side portions thereof, said rolling groove extending in an axial direction of the guide rail; a slider including a plurality of rolling element rolling grooves respectively opposed to said rolling element rolling grooves of said guide rail, said slider being supported on said guide rail in such a manner that said slider is movable along the axial direction of said guide rail through the rolling movements of said rolling elements respectively inserted between said rolling element rolling grooves of said guide rail and said rolling element rolling grooves of said slider, said slider including a rolling element endless circulation track along which said rolling elements are allowed to circulate endlessly; and a plurality of separators, each interposed between said adjoining rolling elements in the circulation direction of said rolling elements. A clearance is formed between a line of said rolling elements and said separators which are endlessly circulated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a linear guide device using therolling movements of balls.

[0003] 2. Description of the Related Art

[0004] Conventionally, as a linear guide device of this type, forexample, as shown in FIG. 8, there is known an apparatus comprising aguide rail 301 elongated in the axial direction thereof and a slider 302which is movably mounted on the guide rail 301 in such a manner that itstraddles over the two side portions of the guide rail 301. In the twoside surfaces of the guide rail 301, there are formed rolling elementrolling grooves 303 respectively extending in the axial direction of theguide rail 301. In a slider main body 302A of the slider 302, there areformed rolling element rolling grooves (not shown) at the respectiveinner surfaces of the two sleeve portions 304 thereof in such a manneras to be respectively opposed to the rolling element rolling grooves 303of the guide rail 301.

[0005] And, between the mutually opposing rolling element rollinggrooves, there are rollably interposed a large number of steel balls Kserving as rolling elements, and the slider 302 is able to move on theguide rail 101 along the axial direction of the guide rail 301 throughthe rolling movements of the balls K. As the slider 302 moves, the ballsK interposed between the guide rail 301 and slider 302 roll and move tothe end portion of the slider main body 302A of the slider 302. However,in order to be able to move the slider 302 continuously in the axialdirection of the guide rail 301, the balls K must circulate endlessly.

[0006] In view of this, not only, within the two sleeve portions 304 ofthe slider main body 302A, there are further formed linear-shapedthrough holes (not shown) respectively extending through theirassociated sleeve portions in the axial direction of the slider mainbody 302A and serving as a rolling element passage, but also two endcaps 305 are respectively disposed on the two front and rear endportions of the slider main body 302A and, in the two end caps 305,there are formed rolling element circulation passages (not shown) whichare respectively curved in a semi-arc shape and allow theabove-mentioned two groups of rolling element rolling grooves and thethrough holes serving as the rolling element passages to communicatewith each other, thereby forming a rolling element endless circulationtrack.

[0007] Also, as shown in FIG. 19, between the two mutually adjoiningones of the balls K in the rolling element endless circulation track, aseparator T including, in its two side surfaces, recessed portions Wrespectively opposed to the two mutually adjoining balls K is interposedin such a manner that the two balls K are respectively contacted withtheir associated recessed portions W of the separator T. The separatorsT are used to eliminate the clearances of the line of the steel balls ofthe rolling element endless circulation track in the circulatingdirection thereof to apply compression forces to the line of the steelballs, thereby enhancing the efficiency of the operation of the linearguide device.

[0008] In the above-mentioned conventional linear guide device, therolling element endless circulation track is composed of a plurality ofcomponents. To absorb variations in the track length of each productcaused by the working errors of the components as well as to forciblyapply the compression forces to the line of the steel balls, there arerequired specifications for a separator having a highly accurate andcomplicated shape (for example, a separator including an elastic portionand a movable portion). However, such separator is difficult tomanufacture.

[0009] Also, in the conventional linear guide device, the separators areset such that they apply the compression force forcibly to the line ofsteel balls. Therefore, when an excessive compression force is appliedto the line of steel balls due to the working errors of the components,the efficiency of the operation of the steel balls is greatly worsenedand also there is generated a harsh grating noise.

[0010] Further, the separator T is structured in such a manner that itstwo outer peripheral surfaces Q are respectively formed as sphericalsurfaces and the two recessed portions W each formed a spherical-shapedsurface are disposed in the two end portions of the separator T whichare respectively in contact with the two balls K. Also, the separator Tis further structured in such a manner that the radius of curvature ofeach of the recessed portions W to be contacted with the balls K is setlarger than the radius of the ball K. Further, the condition of contactbetween the separator T and ball K is specified so that forces actingbetween them are allowed to balance well with each other.

[0011] However, in the linear guide device shown in FIG. 18, the radiusof curvature of each recessed portion W of the separator T to becontacted by the ball K is larger than the radius of the ball K.Therefore, in such a curved track as shown in FIG. 7, the ball K iscontacted with the recessed portion W on the inner side of the curvedtrack to thereby press against the separator T inwardly of the curvedtrack. Thus, the outer peripheral portion Q of the separator T ispressed against a guide member J which forms the inside track surface ofthe curved track. Due to this, there is generated friction between theseparator T and guide member J, which worsens the operation performanceof the ball K and causes noises as well as deteriorates the durabilityof the separator T.

[0012] On the other hand, in the rolling element endless circulationtrack, the balls, which have moved through a linear track (where a loadis applied to the balls) formed of the rolling element rolling groovesfor the purpose of linear guidance, enter a curved track formed of therolling element circulation passages, leave this curved track, and thenmove through another linear track (where the balls are free from anyload). And, the curved track portion (where the balls are free from anyload) and the linear track portion (where the balls are free from anyload) are also referred to as circulation passages.

[0013] In the linear guide device, as an apparatus aiming at enhancingthe efficiency of the operation of balls, for example, there are knownan apparatus which is disclosed in Japanese Utility Model UnexaminedPublication No. 59-103928 of Showa (which is hereinafter referred to asthe conventional example 1) and an apparatus disclosed in JapanesePatent Examined Publication No. 63-8330 of Showa (which is hereinafterreferred to as the conventional example 2).

[0014] Of the two conventional examples, the conventional example 1 isstructured such that, of outside guide members referred to as end capsforming the outside ball contact surfaces of the curved track in thecirculation passages, the leading end portions thereof with which theballs are firstly contacted are set at positions where the outside guidemembers are contacted with the balls moving through the linear trackwhile receiving a load, thereby reducing the impact of the balls againstthe leading end portions of the outside guide members when the balls arecontacted therewith, so that the efficiency of the operation of theballs can be enhanced.

[0015] Also, the conventional example 2 is structured such that there isdisposed a retainer in the entrance of each of the circulation passagesso that the ball is scooped up with the retainer, to thereby reduce theimpact of the ball against the circulation passage or curved track whenthe ball enters it from the linear track, so that the efficiency of theoperation of the balls can be enhanced.

[0016] As described above, these conventional examples, in order toenhance the efficiency of the operation of the balls, aim at preventingthe possibility that the balls can be arranged not in order butalternately, that is, preventing the so-called reeling movements of theballs; or, aim at achieving the smooth revolutions of the balls throughthe circulation track. However, these conventional examples do not aimat reducing the level of the noise caused by the collision of the balls.On the other hand, the present invention points out that the main causeof the noise produced in the conventional linear guide device includingthe above-mentioned circulation passages is closely related with thecollisions, within the circulation passages, of the balls with thevarious guide members forming the circulation passages and, especially,the noise is closely related with the amount of the play allowance ofthe ball in an entrance portion through which the ball moves from thelinear track to the curved track or in an exit portion through which theball moves out of the curved track, in both of which the ballcirculation track becomes unstable.

[0017] In other words, referring to the collision of the ball which isthe main cause of the noise, in order to reduce the noise, there can beexpected two methods: that is, one is to reduce the collision force ofthe ball; and, the other is to reduce the number of times of collisionsof the ball. Here, the collision force reducing method has demerits aswell for the following reasons. Thus, the invention aims at achievingnot only noise level reduction but also enhanced ball operationperformance by employing the method for reducing the number of times ofcollisions of the ball, which is easier than the former method. By theway, the most effective technique to reduce the ball collision forcegreatly is to decrease the mass of the ball which collides with theguide members and guide rail. However, to reduce the diameter of theball incurs a demerit to reduce the load capacity of the linear guidedevice, while use of a ball having low specific gravity such as aceramic ball involves a demerit to cause an increase in the cost of thelinear guide device. Also, only to change the ball scoop-up structure isnot be able to change the collision energy of the ball at all. That is,to reduce the mass of the ball does not seem to be able to provide agreat effect in the noise level reduction.

[0018] In view of the above-mentioned facts, the conventional exampleswill be checked below in detail. In both of the conventional examples 1and 2, the ball collision force in the scoop-up portion can be reducedto a slight degree but the number of times of collisions cannot bereduced, so that there cannot be obtained a great effect for thereduction of the noise level.

[0019] For example, in FIG. 9 which shows a portion of the conventionalexample, there is shown a structure in which a ball B moving within alinear track is scooped up in the leading end portion of a curved trackoutside guide member A, to thereby guide the ball B into a curved track,that is, a circulation passage. The ball contact surface of a curvedtrack inside guide member C is set rather inwardly of the curved track,and the ball contact surface of the curved track outside guide member Ais set rather outwardly of the curved track, thereby giving the ball B aplay allowance. For example, the play allowance Dβ of the ball B, whichhas moved by a phase β from the linear track and is thus present in thevicinity of the entrance of the curved track and is free from any load,is larger than the play allowance Dα of the ball B which has moved by aphase α from the linear track to the curved track and is thus free fromany load, because there is removed the restriction by the outside guidemember. That is, the ball B has, as the maximum value on the ballcirculation track, the play allowance Dβ equal to or larger than theplay allowance Dα of the ball B that has been initially set in design.The ball B, which has played with the maximum play allowance Dβ and isnow present in the vicinity of the entrance of the curved track, thatis, has been displaced greatly from its original position, is thenrestricted to a state where the ball B is free from any load but isgiven the small play allowance Dα, or to the state where the ball B isgiven a load but any play allowance is not given. Then, the ball B willbe collided with its peripheral guide members A, C and guide rail withgreater shocks than the initially set design value, with the result thatthere can be generated the noise.

[0020] Also, in the conventional example 1, in order to achieve itsstructure, the guide member forming the linear track, that is, the ballrolling grooves in the guide rail must be made excessively shallow,which results in the reduced load capacity of the structure; and, due tothe high accuracy of the respective parts and the high working accuracythereof, it is very difficult to manufacture the structure employed theconventional example 1. On the other hand, in the conventional example2, due to the high accuracy of the respective members and the severeworking errors thereof, the originally expected ball scoop-up cannot beattained, which has an ill effect on the operation performance of theballs used in the structure of the conventional example 2.

SUMMARY OF THE INVENTION

[0021] The present invention aims at eliminating the drawbacks found inthe above-mentioned conventional linear guide device. Accordingly, it isan object of the invention to provide a linear guide device which isable to reduce the noise positively and easily or improve separatordurability while realizing enhancement in operation performance.

[0022] To solve the above object, according to the first aspect of theinvention, there is provided a linear guide device including: aplurality of rolling elements; a guide rail extending in an axialdirection thereof and including a plurality of rolling element rollinggrooves in two side portions thereof, the rolling groove extending in anaxial direction of the guide rail; a slider including a plurality ofrolling element rolling grooves respectively opposed to the rollingelement rolling grooves of the guide rail, the slider being supported onthe guide rail in such a manner that the slider is movable along theaxial direction of the guide rail through the rolling movements of therolling elements respectively inserted between the rolling elementrolling grooves of the guide rail and said rolling element rollinggrooves of the slider, the slider including a rolling element endlesscirculation track along which the rolling elements are allowed tocirculate endlessly; and a plurality of separators, each interposedbetween the adjoining rolling elements in the circulation direction ofthe rolling elements, wherein a clearance is formed between a line ofthe rolling elements and the separators which are endlessly circulated.

[0023] Further, according to the second aspect of the invention, thereis provided a linear guide device comprising: a plurality of balls; aguide member defining a curved track which guides the balls; and aseparator interposed between the adjoining balls and having concaveportions in both end portions of the separator in an axial directionthereof, which respectively contacting with the spherical surfaces ofthe adjoining balls, wherein the separator is disposed so that the axisof the separator is parallel to or coincide with a first straight lineconnecting the center points of the adjoining balls, when the balls movealong the curved track, the axis of the separator coincides with thefirst straight line connecting the center points of the adjoining balls,when the balls moves along the curved track, the separators defines asecond straight line connecting the most-outer points of the concaveportions in the adjoining separators interposing the ball, and passingthrough the center point of said interposed ball, the most-outer pointbeing a point contacting with the spherical surface of the ball at anouter periphery side of the curved track, the outer diameter dimensionof the separator having a radius equal to a distance from the outer-mostpoint to the first straight line is set as the minimum outside dimensionof the separator, and the outer diameter dimension of the separator whenthe outer peripheral portion of the separator is contacted with theinside guide member is set as the maximum outside dimension of theseparator.

[0024] Moreover, according to the third aspect of the invention, thereis provided a linear guide device comprising: a plurality of balls; aguide member defining a curved track which guides the balls; and aseparator interposed between the adjoining balls and having concaveportions in both end portions of the separator in an axial directionthereof, which respectively contacting with the spherical surfaces ofthe adjoining balls, wherein the separator is disposed so that the axisof the separator is parallel to or coincide with a first straight lineconnecting the center points of the adjoining balls, and the outsidediameter is set 0.6-0.8 times the diameter of the ball.

[0025] Further, according to the fourth aspect of the invention, thereis provided a linear guide device comprising: a plurality of balls; anda guide member defining a curved track and first and second lineartracks which guide the balls, the balls entering the curved track fromthe first linear track and leaving the curved track into the secondlinear track, wherein the play allowance of each of the balls in atleast one of an entrance portion through which said ball enters thecurved track and an exit portion through which said ball leaves thecurved track is set smaller than the play allowance of the ball within acirculation passage where the ball is free from a load.

[0026] Moreover, according to the fifth aspect of the invention, thereis provided a linear guide device comprising: a plurality of balls; anda guide member defining a curved track and first and second lineartracks which guide the balls, the balls entering the curved track fromthe first linear track and leaving the curved track into the secondlinear track, wherein the play allowance of each of the balls in atleast one of an entrance portion through which said ball enters thecurved track and an exit portion through which the ball leaves thecurved track is set in the range of 0.5 to 11% of the diameter of saidball.

[0027] By the way, in this specification, the term “play allowance”means the allowed amount of the movement of a ball in a direction atright angles to a direction in which the ball is originally expected tomove. Also, the expression “the play allowance of the ball within acirculation passage where the ball is free from a load” means, forexample, in the curved track, the play allowance of the ball in aportion where the movement of the ball in a direction at right angles tothe advancing direction of the ball along its circulatory track isrestricted by the two inside and outside guide members, or the playallowance of the ball in a linear track portion which serves as a returnpassage for the ball.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIGS. 1A and 1B are explanatory views of a rolling element endlesscirculation track employed in a linear guide device according to a firstembodiment of the invention, FIG. 1A is a view showing the phaseposition of steel balls in which the dimension of a clearance formedbetween steel balls and separators in the rolling element endlesscirculation track becomes the smallest, and FIG. 1B is a view showingthe phase position of the steel ball in which the dimension of aclearance formed between the steel balls and separators in the rollingelement endless circulation track becomes the largest;

[0029]FIG. 2 is an explanatory view of an undesirable condition causedwhen the dimension of a clearance formed between the steel balls and theseparator becomes excessively large;

[0030]FIG. 3 is a section view of a separator according to the firstembodiment of the invention;

[0031]FIGS. 4A to 4E are graphs showing variations in dynamic frictionalforces for the respective clearance dimensions as well as variations indynamic frictional forces when no separator is used;

[0032]FIG. 5 is a graph of the relationship between the clearancedimension and the maximum variation component;

[0033]FIG. 6 is a section view of a curved track portion of a linearguide device according to a second embodiment of the invention;

[0034]FIG. 7 is an explanatory view of an inside guide member of alinear guide device according to a third embodiment of the invention;

[0035]FIG. 8 is a section view of a curved track portion which isstructured with the inside guide member shown in FIG. 7;

[0036]FIGS. 9A to 9E are explanatory views showing variations infrictional forces used to evaluate the operation performance of theseparator by the outside dimensions of the separator with respect to thediameter of a ball;

[0037]FIG. 10 is an explanatory view of the evaluation of the respectiveoutside dimensions of the separator with respect to the ball diameter;

[0038]FIG. 11 is a section view of a curved track doorway portion of alinear guide device according to a fourth embodiment of the invention;

[0039]FIG. 12 is a section view of a curved track doorway portion of alinear guide device according to a fifth embodiment of the invention;

[0040]FIG. 13 is a section view of a curved track doorway portion of alinear guide device according to a sixth embodiment of the invention;

[0041]FIG. 14 is an explanatory view of noise levels used to evaluatethe play allowances with respect to the diameters of the ball (thediameters of the steel ball) in the curved track doorway portion;

[0042]FIG. 5 is an explanatory view of ball positions and the sizes ofthe ball play allowances with respect to the ball diameters;

[0043]FIG. 16 is a graph of the relationship between the ball positionsand the sizes of the ball play allowances with respect to the balldiameters (steel ball diameters) shown in FIG. 15;

[0044]FIG. 17 is a perspective view of an end cap of a linear guidedevice according to another embodiment of the fourth to sixthembodiments of the invention;

[0045]FIG. 18 is a general view of a linear guide device;

[0046]FIG. 19 is a section view of a curved track portion employed inthe conventional linear guide device shown in FIG. 18; and

[0047]FIG. 20 is a section view of a curved track doorway portion of aconventional linear guide device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] Now, a description will be given below of a linear guide deviceaccording to a first embodiment of the invention with reference to theaccompanying drawings. By the way, the linear guide device according tothe first embodiment is different from the conventional linear guidedevice shown in FIG. 18 only in separators which are respectivelydisposed between mutually adjoining steel balls in a rolling elementendless circulation track. Therefore, a description will be given belowof only the different portions thereof.

[0049] As shown in FIGS. 1A and 1B, there are employed a plurality ofseparators 10 in such a manner that each separator 10 is interposedbetween two mutually adjoining steel balls B in the rolling elementendless circulation track 7. The separator 10 is formed of materialexcellent in injection moldability and wear resistance, such as 66 nylonor whisker-containing 66 nylon in a short cylindrical shape. As shown inFIG. 3, in the two end faces of the separator 10 in the axial directionthereof, there are formed concave surfaces 11 each having a radius ofcurvature R approximate to the radius of the steel ball. In theconventional structure, the concave surface 11 is contacted with theball B to hold the steel ball B as well as there are eliminatedclearances in the line of steel balls, so as to apply the compressionforce to the line of steel balls. On the other hand, in the presentembodiment, there are formed a clearance in the line of steel balls Band the separators 10, and the thickness d of the separator in the axialdirection is set in such a manner that the clearance and a span betweenthe steel balls B can respectively provide proper values.

[0050] Here, as can be understood from FIGS. 1A and 1B, the dimension ofthe clearance formed between the steel balls B and separators 10 in therolling element endless circulation track 7 varies in accordance withthe phases of the steel balls B. In this embodiment, at the position(the position shown in FIG. 1A) of the phase of the steel balls B wherethe dimension of the clearance between the steel balls B and separators10 becomes the smallest, the dimension of the clearance is set in therange of 2% to 63% of the diameter of the steel ball B. The clearancedimension in this range is regarded as a proper value.

[0051] In case where the dimension of the clearance exceeds 63% of thediameter of the steel ball B, the dimension of the clearance becomes toolarge and, as shown in FIG. 2, there is a possibility that the separator10 can fall down in the semi-arc shaped rolling element circulationpassage 6 of the rolling element endless circulation track 7 and thusthe outer peripheral edge (the boundary portion of the concave surfaceand the outer peripheral surface) A of the end face of the separator 10on the clearance side thereof can be situated upwardly of a straightline (a portion shown by a dotted line in FIG. 2) connecting the twoadjoining steel balls B to bite into the steel ball B in a wedge-likemanner, thereby worsening the operation performance of the linear guidedevice.

[0052] On the other hand, in case where the dimension of the clearanceis less than 2% of the diameter of the steel ball B, the clearancedimension becomes too small and, therefore, there is a possibility that,due to variations in the clearance of the line of steel balls causedaccording to the phases of the steel ball B, an excessive compressionforce can be applied to the steel balls line, thereby worsening theoperation performance of the linear guide device.

[0053] By the way, while the proper range of the clearance dimension(that is, 2% to 63% of the diameter of the steel ball B) is obtainedexperimentally based on the geometrical relation, the lower limit valueof the proper range (that is, 2% of the diameter of the steel ball B) isalmost identical with a calculational value; and, on the other hand, theupper limit value (63% of the diameter of the steel ball B) is abouttwice as large as a calculational value. This is because, practically,all clearances can hardly concentrate on a portion in the line of steelballs but the clearances are arranged scatteringly between the steelballs B to a certain degree.

[0054] Now, FIGS. 4A to 4D respectively show the actually measuredresults of variations in the dynamic frictional forces when the valuesof the clearance dimension/steel ball diameter are set as 0, 0.27, 0.8,and 1.0, and FIG. 4E shows the actually measured results of variationsin the dynamic frictional force when no separator is used. Also, FIG. 5shows the relationship between the clearance dimension/steel balldiameter and the maximum variation component.

[0055] As can be seen clearly from FIG. 5, since the value of themaximum variation component when no separator is used is of the order of0.23 kgf, in case where a condition when the separators are used isassumed to be lower than this, it can be understood that the clearancedimension between the separators 10 and steel balls B may be preferablyset in the range of 2% to 63% of the diameter of the steel ball B.

[0056] AS described above, in the present embodiment, since there areformed clearances in the line of steel balls, even if there are foundworking errors in the respective components which form the rollingelement endless circulation track 7, it is possible to prevent anexcessive compression force from being applied to the line of steelballs. Accordingly, not only a good operation performance can beprovided but also noise reduction can be realized.

[0057] Also, it is not necessary to provide the elastic portion ormovable portion in the separator 10, but the separator 10 may have asimple shape, so that the separator 10 can be manufactured easily and ata low cost.

[0058] By the way, in the above-mentioned embodiment, there is taken acase in which, between two mutually adjoining steel balls, there isinterposed an independent separator 10. However, this is not limitativebut, of course, even in a case where separators 10 are connected to oneanother, there can be obtained similar operation and effects by settinga clearance in the above-mentioned proper range.

[0059] Also, in this embodiment, there is employed a cylindrical-shapedseparator 10. However, the invention is not limited to this but therecan be employed separators having different shapes, for example, aseparator having a cylindrical shape.

[0060] Further, in the above embodiment, the shape of the concavesurface 11 of the separator 10 is set as an R shape having a curvatureapproximate to the radius of the steel ball. However, this is notlimitative but, for example, the shape of the concave surface 11 mayalso be a conical shape or a Gothic arch shape.

[0061] As can be clearly understood from the foregoing description,there can be obtained an effect that enhancement in operationperformance as well as noise reduction can be realized positively andeasily at a low cost.

[0062] Now, a description will be given below of a linear guide deviceaccording to a second embodiment of the invention with reference to theaccompanying drawings.

[0063]FIG. 6, shows a curved track portion of balls 103, which iscomposed of an outside guide member 101 called an end cap and an insideguide member 102 called a return guide. Each ball 103, which has movedthrough a linear track, is turned by 180° in its direction at the curvedtrack portion and is then allowed to move again through a differentlinear track. The ball contact surface of the inside guide member 102forming the curved track is formed as a simple semi-arc shape which isconcentric with the ball contact surface of the outside guide member101.

[0064] In the present embodiment, a column-shaped separator 104 isinterposed between two mutually adjoining balls 103 in such a mannerthat the axis L of the separator 104 is coincident with a straight lineconnecting together the respective centers O of the two mutuallyadjoining balls 103. Each separator 104 includes two concave surfaceportions which are respectively formed at the two end portions of theseparator 304 in the axial direction thereof; and, each of theconcave-surface portions is formed as a spherical-surface recessedportion having a radius of curvature equal to the radius of curvature ofthe spherical surface of the ball 103. However, the shape of theconcave-surface portion is not limited to this and there can be employedany one of other proper shapes, provided it is formed in such a mannerthat at least a portion of the concave-surface recessed portion of theseparator 104, which is located in the vicinity of the outer peripheralportion thereof, can be contacted with the spherical surface of the ball103. And, the shape of the main body of the separator 104 is not alwayslimited to the column shape but it may also be a hollow cylindricalshape, or a spherical shape. What is necessary, as will be discussedlater, is that the shape of the separator 104 allows the separator 104to hold the ball 103 easily and increase the allowance of holding of theball 103 by the separator 104. In view of the above-mentioned condition,with regard to the shape of the separator 104, the outer peripheralsurface of the separator 104 has an advantage in a solid cylindricalshape compared with a spherical shape. Further, it is also advantageousto employ such a shape that the balls 103 can be contacted with theconcave surfaces of the concave-surface recessed portion of theseparator 104, which are located in a position closer to the outerperipheral portions thereof.

[0065] And, in the second embodiment, the outer diameter of the outerperipheral portion of the separator 104 is defined in the followingmanner. That is, the radius of curvature of each of the twospherical-surface recessed portions respectively formed in the two endportions of the separator 104 in the axial direction thereof is setequal to, for example, the radius of curvature of the spherical surfaceof the ball 103. Further, the axis L of the separator 104 is set so asto coincide with a straight line which connects together the centerpoints O of the two mutually adjoining balls 103.

[0066] This definition keeps the relative position relationship betweenthe ball 103 and separator 104 to thereby restrict or prevent theseparator 104 or ball 103 from moving out of position. When looking atthis requirement from a different aspect, assuming that, while the ball303 is moving the curved track, the outer-most points A of the curvedtrack, at which the two spherical-surface recessed portions respectivelyformed in the two end portions of the separator 104 in the axialdirection thereof are in contact with the spherical surface of the balls103, are connected by a straight line S. And, the outside dimension ofthe separator 104 having a radius, which is equal to a distance from thepoints A to the straight line connecting together the center points ofthe two mutually adjoining balls 103 when the straight line S passesthrough the center point of the ball 103 interposed between the twomutually adjoining separators 104, is set as the minimum outer diameterdimension D_(MIN). The actual outside dimension of the separator 104must be larger than the minimum outer diameter dimension D_(MIN). In thecurved track portion through which the ball 103 is allowed to circulatewith no load, there is generally formed a clearance (play allowance)with respect to the ball 103 in view of the smooth circulation of theball and an allowable dimension accuracy. And, in some cases, the ballcontact surface of the outside guide member 101, as shown by a brokenline in FIG. 6, is set rather outwardly of an ideal curved track. Insuch case, in case where the outside dimension of the separator 104 issmaller than the minimum outer diameter dimension D_(MIN), when the ball103 comes into contact with the ball contact surface of the outsideguide member 101 as shown by the broken line in FIG. 6, the separators104 are unable to hold the ball 103 between them within the curved trackportion and thus the ball 103 slips off the separators 104. As a resultof this, not only the position relationship between the ball 103 andseparator 104 is varied but also the respective contact conditions ofthe ball 103 with the separators 104, outside guide member 101 andinside guide member 102 are varied, which results in the generation ofnoises and deteriorated operation performance of the ball as well as theshortened durability of the separator. In view of this, in the secondembodiment, the outside dimension of the separator 104 is set as a valuelarger than the minimum outer diameter dimension D_(MIN) that is definedin the above-mentioned manner.

[0067] On the other hand, the allowable maximum outside dimensionD_(MAX) of the separator 104 is restricted by its interference with theguide members, especially by the inside guide member 102. That is, inthe second embodiment, since the axis of the separator 104 is set so asto coincide with the straight line connecting together the center pointsO of the two mutually adjoining balls 103, in case where the outsidedimension of the separator 104 is set large, the outer peripheralportion of the separator 104 approaches the inside guide member 102.And, if the outside dimension of the separator 104 is excessively large,then the separator 104 and inside guide member 102 interfere with eachother. If the separator 104 is contacted with the inside guide member102, similarly to the above-mentioned case, there are generated noisesas well as the operation performance of the ball and the durability ofthe separator can be lowered. Therefore, the allowable maximum valueD_(MAX) of the outside dimension of the separator 104 is a value atwhich the separator 104 comes into contact with the guide members.

[0068] However, to increase the outside dimension of the separator 104means to increase the surface of the separator 104 to be contacted withthe ball 103 and to increase the holding allowance of the separator 104for holding the ball 103, which can enhances the stable ball holdingability of the separator 104: that is, the larger the outside dimensionof the separator 104 is, the more advantageous. Thus, in case where thisis viewed from the opposite side, for example, in case where the radiusof curvature of the ball contact surface of the inside guide member 102is set large, even if the outside dimension of the separator 104 is setlarger than the above-defined value, there is eliminated the possibilitythat the outer peripheral portion of the separator 104 can come intocontact with the inside guide member 102.

[0069] Next, a description will be given below of a third embodiment ofa linear guide device in which the outer diameter dimension of theseparator 104 is set as large as possible as described above withreference to FIGS. 7 and 8.

[0070] In the third embodiment, the axis L of the separator 104 is setso as to coincide with the straight line connecting together the centerpoints O of the two mutually adjoining balls 103 as well as the secondembodiment. Thus, when the outer diameter dimension of the separator 104is increased, as shown in FIG. 8, in the doorway of the curved track,the outer diameter of the present separator 104 can be made to increaseon until the outer periphery of the separator 104 comes intointerference with the inside guide member 102. In this manner, in casewhere the shape of the inside guide member 102 is designed from a simplesemicircular shape to such a shape as shown in FIG. 7, the outerdiameter of the separator 104 can be made larger than that employed inthe second embodiment. Besides this, there is also available a techniquein which the curved track itself is made large; however, this techniquealso has a demerit that the linear guide device itself increases indimension in the transverse direction thereof.

[0071] Here, there is taken an example of the shape of the ball contactsurface of the inside guide member 102. That is, the shape of the ballcontact surface of the inside guide member 102, which, when the outsidedimension of the separator 104 is set in the above-mentioned manner,prevents the inside guide member 102 from coming into contact with theouter peripheral portion of the separator 104, is firstly defined by twoupper and lower sections having a radius R₂ which are respectively shownin FIG. 7. The two radius R₂ upper and lower sections are respectivelyconnected by a relatively small radius R₃ to the linear track portion ofthe ball 103. Further, the two main ball contact surfaces formed ordefined by the radius R₂ are smoothly connected to each other by arelatively small radius R₁.

[0072] Thanks to this structure, as shown in FIG. 8, the ball contactsurface of the inside guide member 102 is moved more inwardly to thecurved track than that shown by a broken line in FIG. 8, which preventsthe outer peripheral portion of the separator 104 having theabove-mentioned allowable maximum outer diameter dimension from cominginto touch with the inside guide member 102. In this case, the ball 103is restricted by the ball contact surface of the outside guide member101 and the spherical-shaped recessed portion of the separator 104, sothat the ball 103 can be held stably. In addition, the shape of the ballcontact surface of the inside guide member 102 can also be set by acombination of, for example, a straight line and an ellipse.

[0073] Next, a description will be given below of the range of thesubstantial outside dimension of the separators respectively shown inthe second and third embodiments with respect to, for example, the outerdiameter of the ball. Here, as the evaluation of the operationperformance of the ball depending on the outside dimension of theseparator, in FIGS. 9B to 9E, there are shown frictional forcesrespectively obtained when the outside dimensions of the separator areset 0.55 times, 0.65 times, 0.75 times and 0.85 times the diameter ofthe ball. Also, in FIG. 9A, there is shown a frictional force when noseparation is used. Of the variations in the frictional forcesrespectively shown in these figures, FIG. 9B shows a sharp variationwhich is referred to as a beard. The sizes of the maximum variationcomponents (the maximum beard components) in the respective outsidedimensions of the separator are compared with one another, and thecomparison results are shown in FIG. 10. From the fact that the size ofthe maximum variation component in the absence of the separator is ofthe order of 0.5 kgf, it is found that, in case where the condition foruse of the separator is set equal to or less than this size, the outsidedimension of the separator may be set preferably in the range ofsubstantially 0.6 to 0.8 of the diameter of the ball.

[0074] As can be seen obviously from the second and third embodiment,while balls are moving along a curved track, the axis of a separator ismade to coincide with a straight line connecting together the centerpoints of the two mutually adjoining balls interposing the separator.Further, while the balls are moving along the curved track, two points,which are present on the curved track and provide the outer-most pointsof the concave-surface portions of two separators which adjoin eachother with any one of the balls interposed between them and arerespective contacted with the spherical surface of the thus held ball,are connected together by a straight line. Then, the outer diameterdimension of a separator having a radius equal to a distance from theouter-most point to a straight line connecting the center points of thetwo mutually adjoining balls when the straight line connecting betweenthe outer-most points passes through the center point of the ball heldby the two mutually adjoining separators is set as the minimum value ofthe outside dimension of the present separator, whereby the position ofthe ball moving along the curved track can be restricted accurately. Incombination with this, the outer diameter dimension of a separator whenthe outer periphery of the separator comes into contact with the guidemember forming the curved track is set as the maximum value of the outerdiameter dimension of the separator, so that, in a range in which theseparator is prevented from coming into contact with the guide member,the outer diameter dimension of the separator can be increased tothereby be able to enhance the ball holding function of the separator,enhance the operation performance of the ball, reduce the level ofnoises caused by the ball, and enhance the durability of the separator.

[0075] Next, a description will be given of a fourth embodiment of theinvention with reference to the accompanying drawings. Specifically,FIG. 11 is an explanatory view of a connecting portion between a lineartrack portion and a curved track portion for a ball (steel ball) 203.The linear track portion is composed of a linear track inside guidemember 205 called a rail and a linear track outside guide member 206called a bearing. The curved track portion is composed of a curved trackoutside guide member 201 called an end cap and a curved track insideguide member 202 called a return guide. In this embodiment, the ball 203moved through the linear track enters the curved track, and then theball 203 is turned by 180°, so that the ball leaves the present curvedtrack and moves again through another linear track. Therefore, here, thecurved track portion forms part of a circulation passage. By the way,according to the present embodiment, the linear track outside guidemember 206 and curved track inside guide member 202 are formedseparately from each other. Also, the end portion of the curved trackoutside guide member 101 on the linear track side thereof is sharpened,and the sharpened leading end portion of the curved track outside guidemember 201 is inserted into the inside portion of the linear trackinside guide member 205, whereby the ball 203 moving through the lineartrack can be guided and scooped up into the curved track. Also, the ballcontact surface of the curved track outside guide member 201 is formedin a simple semi-arc shape.

[0076] In the present embodiment, except for the portions of the curvedtrack outside guide member 201 and curved track inside guide member 202where the ball 203 is positioned in a phase γ after the ball 203 hasmoved from the linear track to the curved track (that is, after the ball203 has passed through a point δ shown in FIG. 11), similarly to theconventional art, the ball contact surface of the curved track insideguide member 202 is set rather inwardly of the curved track, the ballcontact surface of the curved track outside guide member 201 is setrather outwardly of the curved track. Further, there is formed the sameplay allowance Dα as the play allowance in the conventional art in adirection at right angles to the original moving direction of the ball203.

[0077] And, in the conventional examples, at the same time when the ballhas moved from the linear track to the curved track, the ball contactsurface of the curved track inside guide member 202 is set ratherinwardly of the curved track. However, on the other hand, according tothe present embodiment, while the ball is present in the phase γ fromthe transition point δ between the linear track and the curved track,that is, until the time when the ball 203 is substantially scooped up bythe curved track outside guide member 201, the ball contact surface ofthe curved track inside guide member 202 is set more outside than in theconventional examples. Due to such setting, the ball play allowance Dβin the curved track doorway in this phase β where the ball playallowance conventionally provides the maximum value (Dα or more) issmaller than the play allowance Dα of the ball 103 within thecirculation passage in which no load is applied to the ball. Here, theterm “the curved track doorway” means, of an angular range from astraight line connecting the center of the curved track inside guidemember 202 with the point of the curved track outside guide member 201,where the scoop-up of the ball 203 is started, to the contact surface ofthe curved track outside guide member 201 with respect to the end faceof the linear track outside guide member 206, that is, of the angularrange of the phase γ, in particular, a portion where the ball 203 isscooped up by the curved track outside guide member 201. In this manner,in case where the play allowance Dβ of the ball 203 in the curved trackdoorway is set small, the play of the ball in this portion is small,that is, the displacement from the ball original position is small.Thus, the number of times that the ball 203 is collided with the curvedtrack outside guide member 201, the curved track inside guide member 202and linear track inside guide member 105 before and behind such curvedtrack doorway is reduced, thereby the noise involved with the collisionsof the ball is also reduced. Also, without increasing the number ofparts and the manufacturing cost of the apparatus, the noise can bereduced easily.

[0078] Further, especially, since the play allowances of the respectiveportions depend on only the relative position relationship between thecurved track outside guide member 201 and curved track inside guidemember 202, for example, there is eliminated the need, as in a fifthembodiment which will be discussed later, to position the linear trackoutside guide member 206 and curved track outside guide member 201 withhigh accuracy, which makes it possible not only to facilitate theassembling operation of the apparatus but also to reduce themanufacturing cost of the apparatus. By the way, the shape in which theball contact surface of the curved track inside guide member 202 isexpanded more outside than in the conventional examples is not limitedto the shape shown in FIG. 11 but, for example, any other shape such asan elliptical shape, an R shape, or a combination of these shaped can beemployed, provided that it allows the ball contact surface of the curvedtrack inside guide member 102 to expand more outwardly than in theconventional examples so that the play allowance DP of the ball 103 inthe curved track doorway portion can be made smaller than that obtainedin the conventional examples.

[0079] Here, FIGS. 15 and 16 show the above-mentioned structure when itis viewed from a different point of view. In the above conventionalexamples, in an A block which provides the load applying side of thelinear track portion, there is not formed such play allowance as shownin FIGS. 15 and 16; in a B block of the curved track portion before theball reaches the phase γ the play allowance of the ball becomes themaximum value; and, in a C block after the ball reaches the phase γ, theplay allowance of the ball becomes a constant play allowance Dα and thusthe C block provides a stable ball circulation track. On the other hand,according to the present embodiment, since the play allowance of theball in the doorway of the curved track is set small, there iseliminated such possibility as in the conventional examples that theplay allowance of the ball can have the maximum value, and the ball playallowance varies almost uniformly, so that the level of the noise causedby the collision of the ball can be reduced.

[0080] Next, a description will be given below of a fifth embodiment ofa linear guide device according to the invention with reference to FIG.12.

[0081] In this embodiment, the center axis of a curved track isdisplaced inwardly from the center axis of a linear track. Due to this,between a phase γ from a transition point 6 transiting from the lineartrack to the curved track, the play allowance Dβ of the ball in a curvedtrack doorway in an arbitrary phase β of the center of the ball can bemade smaller than the play allowance Dα of the ball in a phase α afterthe phase γ in the curved track, where the ball is present within thecirculation passage and thus the ball is free from a load. And, thanksto this setting of the ball play allowances, similarly to the fourthembodiment, the play allowance Dβ of the ball in a curved track doorwaycan be made smaller than that in the conventional examples, which canreduce the number of times of collisions of the balls 203 with thecurved track outside guide member 201, curved track inside guide member202 and linear track inside guide member 205, thereby being able toreduce the level of the noise involved with the collision of the ball.Also, since use of this structure does not increase the number of parts,and also since a method for working the components of the structure isneither so complicated nor so highly accurate, the level of the noisecan be reduced easily while preventing an increase in the manufacturingcost of the apparatus.

[0082] Further, in this embodiment, the ball scoop-up tongue portion(the linear track side end portion of the curved track outside guidemember 201) can be set at a position nearer to the linear track than inthe fourth embodiment, which can reduce the number of times ofcollisions between the guide member, that is, the rail 205 and the ball203, so that the noise level reduction can be realized more effectivelythan the fourth embodiment.

[0083] Next, a description will be given below of a sixth embodiment ofa linear guide device according to the invention with reference to FIG.13.

[0084] In this embodiment, there is disposed an intermediate insideguide member 204 which is composed of a thin metal plate, a wire or asimilar member in a gap between the linear track inside guide member 205and curved track outside guide member 201. The ball 203 is firstlyscooped up by the intermediate inside guide member 204 and is thenguided to the curved track outside guide member 201. That is, the ball203 does not move directly from the linear track inside guide member 205to the curved track outside guide member 201 but, after the ball 203 isonce scooped up by the intermediate inside guide member 204 (theposition of the phase γ), the ball 203 is transferred to the curvedtrack outside guide member 201. Therefore, because the play of the ball203 is restricted by the intermediate inside guide member 204, the playallowance Dβ of the ball in the curved track doorway in a phase βexisting in the phase γ from the transition point δ transiting from thelinear track to the curved track (especially, the portion where the ball203 is scooped up by the intermediate inside guide member 204) can bemade smaller than in the conventional examples, so that the playallowance Dβ of the ball can be made smaller than the play allowance Dαof the ball in its no-load condition within the circulation passage inthe phase α in the curved track after the phase γ. And, due to this,similarly to the fourth embodiment, the play allowance Dβ of the ball inthe curved track doorway is smaller than in the conventional examples,which can reduce the number of times of collisions of the balls 203 withthe curved track outside guide member 201, curved track inside guidemember 202 and linear track inside guide member 205, thereby being ableto reduce the level of the noise involved with the collision of theball. Also, since a method for working the components of the structureis neither so complicated nor so highly accurate, the noise level can bereduced easily while preventing an increase in the manufacturing cost ofthe apparatus. Further, especially, the intermediate inside guide member204 has not only a function to adjust the play allowance of the ball butalso a function to hold the ball to thereby prevent it from slipping outof position.

[0085] In the fourth to sixth embodiments described heretofore, thetongue of the end cap for scooping up the ball is formed in a projectingtype scoop-up shape in which the leading end of the tongue can beinserted into the ball rolling grooves of the guide rail. However, theinvention is not limited to the above-mentioned scoop-up shape but, forexample, the ball rolling grooves of the guide rail can be formedshallow and there can be employed such an end cap as shown in FIG. 17which is formed in a recessed type scoop-up shape (a so called shipbottom type scoop-up end cap).

[0086] Next, a description will be given below of differences betweenthe levels of noises obtained when, in the above-mentioned fourth tosixth embodiments, the play allowances of the ball in the curved trackdoorway, that is, in the circulation passage doorway are changedvariously. FIG. 4 shows noise levels obtained when the greatest value(maximum value) of the play allowance (in FIG. 14, clearance amount) inthe vicinity of the circulation passage doorway is expressed by a ratiowith respect to the ball diameter (in FIG. 14, steel ball diameter), andthe ratio is changed variously. On the other hand, in view of the factthat the noise level of a standard product is about 67 dB, the playallowance in the vicinity of the circulation passage doorway provides anoise level reducing effect in the range of about 0.5% to about 11% ofthe ball diameter and, especially, in the range of about 1.5% to 10%,the noise level reducing effect is large. Also, in case where the playallowance becomes extremely small, the noise level is great. This isbecause the extreme small play allowance induces a so called ball jamand the efficiency of the operation of the ball is thereby lowered. Thiscoincides with an idiomatically used evaluation “that a ball needs acertain degree of play within a circulation passage”.

[0087] As can be obviously understood from the foregoing description,according to the linear guide device of the invention, since the playallowance of the ball in at least one of the entrance of the ball intothe curved track and the exit of the ball from the curved track is setsmaller than the play allowance of the ball within the circulationpassage where the ball is free from a load, the play allowance of theball in the curved track doorway becomes small, which allows the ball tobe guided into the circulation passage along a smooth and stable track,thereby being able to reduce the number of times of collisions of theball with its peripheral members such as the guide members and guiderail, with the result that the level of the noise involved with thecollision of the ball can be reduced as well as the operationperformance of the ball can be enhanced. Also, because the playallowance of the ball in the curved track can be made small withoutrequiring new members as well as without requiring complicated workingor high-accuracy working, the invention can be enforced easily whilepreventing an increase in the manufacturing cost thereof.

[0088] While only certain embodiments of the invention have beenspecifically described herein, it will apparent that numerousmodification may be made thereto without departing from the spirit andscope of the invention.

What is claimed is:
 1. A linear guide device comprising: a plurality ofrolling elements; a guide rail extending in an axial direction thereofand including a plurality of rolling element rolling grooves in two sideportions thereof, said rolling groove extending in an axial direction ofthe guide rail; a slider including a plurality of rolling elementrolling grooves respectively opposed to said rolling element rollinggrooves of said guide rail, said slider being supported on said guiderail in such a manner as to be movable along the axial direction of saidguide rail through the rolling movements of said rolling elementsrespectively inserted between said rolling element rolling grooves ofsaid guide rail and said rolling element rolling grooves of said slider,said slider defining a rolling element endless circulation track alongwhich said rolling elements are allowed to circulate endlessly; and aplurality of separators, each interposed between said adjoining rollingelements in the circulation direction of said rolling elements, whereina clearance is formed between a line of said rolling elements and saidseparators which are endlessly circulated.
 2. A linear guide deviceaccording to claim 1, wherein said rolling elements are balls, and thetotal dimension of said clearances formed between said balls and saidseparators is set in the range of 2% to 63% of the diameter of said ballat a position of the phase of said balls in which the total dimension ofsaid clearances in said rolling element endless circulation track isminimum.
 3. A linear guide device comprising: a plurality of balls; aguide member defining a curved track which guides said balls; and aseparator interposed between said adjoining balls and having concaveportions in both end portions of said separator in an axial directionthereof, which respectively contacting with the spherical surfaces ofsaid adjoining balls, wherein said separator is disposed so that theaxis of said separator coincides with a first straight line connectingthe center points of said adjoining balls, when said balls moves alongsaid curved track, said separators defines a second straight lineconnecting the most-outer points of said concave portions in saidadjoining separators interposing said ball, and passing through thecenter point of said interposed ball, said most-outer point being apoint contacting with the spherical surface of said ball at an outerperiphery side of said curved track, the outer diameter dimension ofsaid separator having a radius equal to a distance from said outer-mostpoint to said first straight line is set as the minimum outsidedimension of said separator, and the outer diameter dimension of saidseparator when the outer peripheral portion of said separator iscontacted with said inside guide member is set as the maximum outsidedimension of said separator.
 4. A linear guide device according to claim3, wherein said separator is formed in a substantially column shape. 5.A linear guide device according to claim 3, wherein said separator isformed in a substantially cylindrical shape.
 6. A linear guide deviceaccording to claim 3, wherein said guide member comprises an insideguide member with a surface defining an inner periphery of said curvedtrack, and said surface of said inside guide member is partially formedin section by an arc by having a radius longer than that of asemi-circular arc.
 7. A linear guide device comprising: a plurality ofballs; a guide member defining a curved track which guides said balls;and a separator interposed between said adjoining balls and havingconcave portions in both end portions of said separator in an axialdirection thereof, which respectively contacting with the sphericalsurfaces of said adjoining balls, wherein said separator is disposed sothat the axis of said separator is parallel to or coincide with astraight line connecting the center points of said adjoining balls, andthe outside dimension of said separator is set 0.6-0.8 times thediameter of said ball.
 8. A linear guide device according to claim 7,wherein said separator is formed in a substantially column shape.
 9. Alinear guide device according to claim 7, wherein said separator isformed in a substantially cylindrical shape.
 10. A linear guide deviceaccording to claim 7, wherein said guide member comprises an insideguide member with a surface defining an inner periphery of said curvedtrack, and said surface of said inside guide member is partially formedin section by an arc by having a radius larger than that of asemi-circular arc.
 11. A linear guide device comprising: a plurality ofballs; and a guide member defining a curved track and first and secondlinear tracks which guide said balls, said balls entering said curvedtrack from said first linear track and leaving said curved track intosaid second linear track, wherein the play allowance of each of saidballs in at least one of an entrance portion through which said ballenters said curved track and an exit portion through which said ballleaves said curved track is set smaller than the play allowance of saidball within a circulation passage where said ball is free from a load.12. A linear guide device according to claim 11, wherein the center axisof said curved track is shifted from the center axes of said first andsecond linear tracks.
 13. A linear guide device according to claim 11,further comprising: an intermediate guide member defining a part of saidcurved track in at least one of the entrance portion and the exitportion so that the play allowance therein is set smaller than that ofsaid ball within the circulation passage where said ball is free fromthe load.
 14. A linear guide device comprising: a plurality of balls;and a guide member defining a curved track and first and second lineartracks which guide said balls, said balls entering said curved trackfrom said first linear track and leaving said curved track into saidsecond linear track, wherein the play allowance of each of said balls inat least one of an entrance portion through which said ball enters saidcurved track and an exit portion through which said ball leaves saidcurved track is set in the range of 0.5 to 11% of the diameter of saidball.
 15. A linear guide device according to claim 14, wherein thecenter axis of said curved track is shifted from the center axes of saidfirst and second linear tracks.
 16. A linear guide device according toclaim 14, further comprising: an intermediate guide member defining apart of said curved track in at least one of the entrance portion andthe exit portion so that the play allowance therein is set in the rangeof 0.5 to 11% of the diameter of said ball.
 17. A linear guide devicecomprising: a plurality of balls; and a guide member defining a curvedtrack and first and second linear tracks which guide said balls, saidballs entering said curved track from said first linear track andleaving said curved track into said second linear track, wherein theplay allowance of each of said balls in at least one of an entranceportion through which said ball enters said curved track and an exitportion through which said ball leaves said curved track is set in therange of 1.5 to 10% of the diameter of said ball.
 18. A linear guidedevice according to claim 17, wherein the center axis of said curvedtrack is shifted from the center axes of said first and second lineartracks.
 19. A linear guide device according to claim 17, furthercomprising: an intermediate guide member defining a part of said curvedtrack in at least one of the entrance portion and the exit portion sothat the play allowance therein is set in the range of 1.5 to 10% of thediameter of said ball.